ZnO/CoO@NiCoS nanohybrids with double heterogeneous interface for high-performance hybrid supercapacitors

Abstract Hybrid supercapacitors (HSC) with high power density and long cycle life are received more attention in the field of energy storage devices, however, the wide application of HSC is limited by the low energy density owing to the insufficient active sites and poor electronic conductivity of electrode materials. Here, we successfully synthesize the ZnO/CoO@NiCoS nanohybrids with double-layer heterojunction by a three-step method. The conductivity of the as-prepared electrode can be improved by the built-in electric field formed between ZnO and CoO. The coating of amorphous NiCoS can provide sufficient active sites and strengthen the physical/chemical stability of ZnO/CoO nanowires. The obtained ZnO/CoO@NiCoS delivers a high specific capacity of 934 C g−1 (1868 F g−1), which is 5.5 times the pristine ZnO electrode. Furthermore, a HSC with ZnO/CoO@NiCoS shows an improved power density (3987.7 W kg−1), a high energy density of 39.2 Wh kg−1, and an excellent cycling stability (initial capacity retention rate of 81.7% after 6,000 cycles). This study not only proposes an effective strategy for the preparation of low-cost, deep-discharge electrodes for supercapacitors, but also provides a novel method to construct nanomaterials with double-layer heterostructure and built-in electric field.